U.S. patent number 6,828,890 [Application Number 10/255,984] was granted by the patent office on 2004-12-07 for high intensity radial field magnetic array and actuator.
This patent grant is currently assigned to Engineering Matters, Inc.. Invention is credited to David B. Cope, Andrew M. Wright.
United States Patent |
6,828,890 |
Cope , et al. |
December 7, 2004 |
**Please see images for:
( Certificate of Correction ) ** |
High intensity radial field magnetic array and actuator
Abstract
A miniature actuator, e.g., for use in a Micro Air Vehicle,
comprises at least one nested array of magnets, with an outer
annular magnet with a magnetization pointing in an axial direction,
a middle annular magnet with a radial magnetization, and an inner
cylindrical magnet with a magnetization directed anti-parallel to
the magnetization of the outer annular magnet. In one embodiment, a
permanent magnet actuator comprises such an array, and a conductive
coil having a current distributed over the volume of the conductive
coil, wherein the magnetic field of the array is perpendicular to
the current located in the coil. The coil may be located above or
below the first magnetic array. In another embodiment, a conductive
coil is disposed between two magnetic arrays. The coil may have a
winding that is pancake-shaped, solenoidal, or toroidal and may
comprise more than one winding. The magnetic arrays may be canted
to permit the toroidal winding to expand, affording control over
the spread of the magnetic field in the gap.
Inventors: |
Cope; David B. (Medfield,
MA), Wright; Andrew M. (Somerville, MA) |
Assignee: |
Engineering Matters, Inc.
(Newton, MA)
|
Family
ID: |
26945084 |
Appl.
No.: |
10/255,984 |
Filed: |
September 26, 2002 |
Current U.S.
Class: |
335/296; 335/222;
335/229; 335/299; 335/306 |
Current CPC
Class: |
H01F
7/20 (20130101); H01F 7/066 (20130101) |
Current International
Class: |
H01F
7/20 (20060101); H01F 7/06 (20060101); H01F
007/00 () |
Field of
Search: |
;335/222,229,234,296-306
;310/90.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Image from PPT presentation, Corcoran Engineering, Apr. 2001, re:
(Linear) Halbach Array Magnet Configuration..
|
Primary Examiner: Barrera; Ramon M.
Attorney, Agent or Firm: Hayes Soloway P.C.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This Application claims priority from U.S. Provisional Application
Ser. No. 60/325,123, filed Sep. 26, 2001.
Claims
What is claimed is:
1. A nested magnetic array comprising: an outer magnet having a
magnetization pointing in an axial direction; a middle magnet
having a radial magnetization substantially perpendicular to the
magnetization of said outer magnet; and an inner magnet having a
magnetization directed substantially anti-parallel to the
magnetization of said outer magnet.
2. The magnetic array of claim 1, wherein the inner magnet, middle
magnet, and outer magnet are cannulated.
3. The magnetic array of claim 1, wherein the inner magnet, is a
solid member.
4. The magnetic array of claim 1, wherein the inner magnet, middle
magnet, and outer magnet are made from NdFeB.
5. The magnetic array of claim 1, wherein the inner magnet, middle
magnet, and outer magnet are made from SmCo.
6. A permanent magnetic actuator comprising: a first magnetic array
comprising nested outer and middle magnets and an inner magnet,
wherein the outer magnet of said first magnetic array has a
magnetization pointing in an axial direction, the middle magnet of
said first magnetic array has a radial magnetization, and the inner
magnet of said first magnetic array has a magnetization directed
substantially anti-parallel to the magnetization of said outer
magnet; and a conductive coil having a current distributed over the
volume of said conductive coil, wherein the magnetic field of said
first magnetic array is substantially perpendicular to said current
in said coil.
7. The permanent magnetic actuator of claim 6, wherein said
conductive coil is located below said first magnetic array.
8. The permanent magnetic actuator of claim 6, wherein said
conductive coil is located above said first magnetic array.
9. The permanent magnetic actuator of claim 6, further comprising:
a second magnetic array comprising nested outer and middle magnets
and an inner magnet, said second magnetic array being located on
the opposite side of said conductive coil from said first magnetic
array, wherein the outer magnet of said second magnetic array has a
magnetization directed substantially parallel to the direction of
the magnetization of the inner magnet of said first magnetic array,
the middle magnet of said second magnetic array has a radial
magnetization in substantially the same direction as the middle
magnet of the first magnetic array, and the inner magnet of said
second magnetic array has a magnetization substantially
anti-parallel to the magnetization of the outer magnet of said
second magnetic array; wherein said conductive coil is disposed
between said first and said second magnetic arrays, and wherein the
magnetic field of said first and said second magnetic arrays is
substantially perpendicular to said current located in said
conductive coil.
10. The permanent magnetic actuator of claim 9, further comprising
annular ferromagnetic flux posts disposed between first and second
magnetic arrays.
11. The permanent magnetic actuator of claim 9, further comprising
ferromagnetic flux posts disposed between first and second magnetic
arrays.
12. The permanent magnetic actuator of claim 9, wherein the
conductive coil is wound in a pancake winding.
13. The permanent magnetic actuator of claim 9, wherein the
conductive coil is wound in a solenoidal winding.
14. The permanent magnetic actuator of claim 9, wherein the
conductive coil is wound in a toroidal winding.
15. The permanent magnetic actuator of claim 9, wherein the
magnetic arrays are canted.
16. The permanent magnetic actuator of claim 9, wherein the
conductive coil is wound with two toroidal windings, such that the
windings have the same poloidal sense but opposite toroidal
sense.
17. The permanent magnetic actuator of claim 9, wherein the
conductive coil is wound with two toroidal windings, such that the
windings have the same toroidal sense but opposite poloidal
sense.
18. The permanent magnetic actuator of claim 6, wherein said
conductive coil comprises at least one wire having a plurality of
turns.
19. The permanent magnetic actuator of claim 18, wherein the
conductive coil is wound with two toroidal windings, such that the
windings have the same poloidal sense but opposite toroidal
sense.
20. The permanent magnetic actuator of claim 18, wherein the
conductive coil is wound with two toroidal windings, such that the
windings have the same toroidal sense but opposite poloidal
sense.
21. The permanent magnetic actuator of claim 6, wherein the inner
magnet, middle magnet, and outer magnet are cannulated.
22. The permanent magnetic actuator of claim 6, wherein the inner
magnet, is a solid member.
23. The permanent magnetic actuator of claim 6, wherein the inner
magnet, middle magnet, and outer magnet are made from NdFeB.
24. The permanent magnetic actuator of claim 6, wherein the inner
magnet, middle magnet, and outer magnet are made from SmCo.
25. The permanent magnetic actuator of claim 6, wherein the
conductive coil is wound in a pancake winding.
26. The permanent magnetic actuator of claim 6, wherein the
conductive coil is wound in a solenoidal winding.
27. The permanent magnetic actuator of claim 6, wherein the
conductive coil is wound in a toroidal winding.
28. The permanent magnetic actuator of claim 6, wherein the
conductive coil is wound with two toroidal windings, such that the
windings have the same poloidal sense but opposite toroidal
sense.
29. The permanent magnetic actuator of claim 28, wherein the
magnetic arrays are canted.
30. The permanent magnetic actuator of claim 6, wherein the
conductive coil is wound with two toroidal windings, such that the
windings have the same toroidal sense but opposite poloidal
sense.
31. The permanent magnetic actuator of claim 30, wherein the
magnetic arrays are canted.
32. A method for creating a magnetic force comprising: creating a
magnetic field engulfing a conductive coil, said magnetic field
comprising the superposition of a first magnetic field curling from
an inner magnet of a magnetic array outward to an outer magnet of
said magnetic array, and a second magnetic field pointing radially
outward from a middle magnet of said magnetic array; and applying a
current through said conductive coil.
33. A nested magnetic array comprising: an outer annular magnet
having a magnetization pointing in an axial direction; a middle
annular magnet having a radial magnetization substantially
perpendicular to the magnetization of said outer annular magnet;
and an inner cylindrical magnet having a magnetization directed
substantially anti-parallel to the magnetization of said outer
annular magnet.
34. The magnetic array of claim 33, wherein the inner cylindrical
magnet, middle annular magnet, and outer annular magnet are
cannulated.
35. The magnetic array of claim 33, wherein the inner cylindrical
magnet, is a solid member.
36. The magnetic array of claim 33, wherein the inner cylindrical
magnet, middle annular magnet, and outer annular magnet are made
from NdFeB.
37. The magnetic array of claim 33, wherein the inner cylindrical
magnet, middle annular magnet, and outer annular magnet are made
from SmCo.
38. A permanent magnetic actuator comprising: a first magnetic
array comprising nested outer and middle annular magnets and an
inner cylindrical magnet, wherein the outer annular magnet of said
first magnetic array has a magnetization pointing in an axial
direction, the middle annular magnet of said first magnetic array
has a radial magnetization, and the inner cylindrical magnet of
said first magnetic array has a magnetization directed
substantially anti-parallel to the magnetization of said outer
annular magnet; and a conductive coil having a current distributed
over the volume of said conductive coil, wherein the magnetic field
of said first magnetic array is substantially perpendicular to said
current in said coil.
39. The permanent magnetic actuator of claim 38, wherein said
conductive coil is located below said first magnetic array.
40. The permanent magnetic actuator of claim 38, wherein said
conductive coil is located above said first magnetic array.
41. The permanent magnetic actuator of claim 38, further
comprising: a second magnetic array comprising nested outer and
middle annular magnets and an inner cylindrical magnet, said second
magnetic array being located on the opposite side of said
conductive coil from said first magnetic array, wherein the outer
annular magnet of said second magnetic array has a magnetization
directed substantially parallel to the direction of the
magnetization of the inner cylindrical magnet of said first
magnetic array, the middle annular magnet of said second magnetic
array has a radial magnetization in substantially the same
direction as the middle annular magnet of the first magnetic array,
and the inner cylindrical magnet of said second magnetic array has
a magnetization substantially anti-parallel to the magnetization of
the outer annular magnet of said second magnetic array; wherein
said conductive coil is disposed between said first and said second
magnetic arrays, and wherein the magnetic field of said first and
said second magnetic arrays is substantially perpendicular to said
current located in said conductive coil.
42. The permanent magnetic actuator of claim 41, further comprising
annular ferromagnetic flux posts disposed between first and second
magnetic arrays.
43. The permanent magnetic actuator of claim 41, further comprising
ferromagnetic flux posts disposed between first and second magnetic
arrays.
44. The permanent magnetic actuator of claim 41, wherein the
conductive coil is wound in a pancake winding.
45. The permanent magnetic actuator of claim 41, wherein the
conductive coil is wound in a solenoidal winding.
46. The permanent magnetic actuator of claim 41, wherein the
conductive coil is wound in a toroidal winding.
47. The permanent magnetic actuator of claim 41, wherein the
conductive coil is wound with two toroidal windings, such that the
windings have the same poloidal sense but opposite toroidal
sense.
48. The permanent magnetic actuator of claim 41, wherein the
conductive coil is wound with two toroidal windings, such that the
windings have the same toroidal sense but opposite poloidal
sense.
49. The permanent magnetic actuator of claim 38, wherein said
conductive coil comprises at least one wire having a plurality of
turns.
50. The permanent magnetic actuator of claim 38, wherein the inner
cylindrical magnet, middle annular magnet, and outer annular magnet
are cannulated.
51. The permanent magnetic actuator of claim 38, wherein the inner
cylindrical magnet, is a solid member.
52. The permanent magnetic actuator of claim 38, wherein the inner
cylindrical magnet, middle annular magnet, and outer annular magnet
are made from NdFeB.
53. The permanent magnetic actuator of claim 38, wherein the inner
cylindrical magnet, middle annular magnet, and outer annular magnet
are made from SmCo.
54. The permanent magnetic actuator of claim 38, wherein the
conductive coil is wound in a pancake winding.
55. The permanent magnetic actuator of claim 38, wherein the
conductive coil is wound in a solenoidal winding.
56. The permanent magnetic actuator of claim 38, wherein the
conductive coil is wound in a toroidal winding.
57. A method for creating a magnetic force comprising: creating a
magnetic field engulfing a conductive coil, said magnetic field
comprising the superposition of a first magnetic field curling from
an inner cylinder of a magnetic array outward to an outer ring of
said magnetic array, and a second magnetic field pointing radially
outward from a middle annular ring of said magnetic array; and
applying a current through said conductive coil.
58. A nested magnetic array comprising: an outer annular magnet
having a magnetization pointing in an axial direction; a middle
annular magnet having a radial magnetization substantially
perpendicular to the magnetization of said outer annular magnet;
and an inner annular magnet having a magnetization directed
substantially anti-parallel to the magnetization of said outer
annular magnet.
59. The magnetic array of claim 58, wherein the inner annular
magnet, middle annular magnet, and outer annular magnet are
cannulated.
60. The magnetic array of claim 58, wherein the inner annular
magnet, is a solid member.
61. The magnetic array of claim 58, wherein the inner annular
magnet, middle annular magnet, and outer annular magnet are made
from NdFeB.
62. The magnetic array of claim 58, wherein the inner annular
magnet, middle annular magnet, and outer annular magnet are made
from SmCo.
63. A permanent magnetic actuator comprising: a first magnetic
array comprising nested outer and middle annular magnets and an
inner annular magnet, wherein the outer annular magnet of said
first magnetic array has a magnetization pointing in an axial
direction, the middle annular magnet of said first magnetic array
has a radial magnetization, and the inner annular magnet of said
first magnetic array has a magnetization directed substantially
anti-parallel to the magnetization of said outer annular magnet;
and a conductive coil having a current distributed over the volume
of said conductive coil, wherein the magnetic field of said first
magnetic array is substantially perpendicular to said current in
said coil.
64. The permanent magnetic actuator of claim 63, wherein said
conductive coil is located below said first magnetic array.
65. The permanent magnetic actuator of claim 63, wherein said
conductive coil is located above said first magnetic array.
66. The permanent magnetic actuator of claim 63, further
comprising: a second magnetic array comprising nested outer and
middle annular magnets and an inner annular magnet, said second
magnetic array being located on the opposite side of said
conductive coil from said first magnetic array, wherein the outer
annular magnet of said second magnetic array has a magnetization
directed substantially parallel to the direction of the
magnetization of the inner annular magnet of said first magnetic
array, the middle annular magnet of said second magnetic array has
a radial magnetization in substantially the same direction as the
middle annular magnet of the first magnetic array, and the inner
annular magnet of said second magnetic array has a magnetization
substantially anti-parallel to the magnetization of the outer
annular magnet of said second magnetic array; wherein said
conductive coil is disposed between said first and said second
magnetic arrays, and wherein the magnetic field of said first and
said second magnetic arrays is substantially perpendicular to said
current located in said conductive coil.
67. The permanent magnetic actuator of claim 66, further comprising
annular ferromagnetic flux posts disposed between first and second
magnetic arrays.
68. The permanent magnetic actuator of claim 66, further comprising
ferromagnetic flux posts disposed between first and second magnetic
arrays.
69. The permanent magnetic actuator of claim 66, wherein the
conductive coil is wound in a pancake winding.
70. The permanent magnetic actuator of claim 66, wherein the
conductive coil is wound in a solenoidal winding.
71. The permanent magnetic actuator of claim 66, wherein the
conductive coil is wound in a toroidal winding.
72. The permanent magnetic actuator of claim 66, wherein the
conductive coil is wound with two toroidal windings, such that the
windings have the same poloidal sense but opposite toroidal
sense.
73. The permanent magnetic actuator of claim 66, wherein the
conductive coil is wound with two toroidal windings, such that the
windings have the same toroidal sense but opposite poloidal
sense.
74. The permanent magnetic actuator of claim 63, wherein said
conductive coil comprises at least one wire having a plurality of
turns.
75. The permanent magnetic actuator of claim 63, wherein the inner
annular magnet, middle annular magnet, and outer annular magnet are
cannulated.
76. The permanent magnetic actuator of claim 63, wherein the inner
annular magnet is a solid member.
77. The permanent magnetic actuator of claim 63, wherein the inner
annular magnet, middle annular magnet, and outer annular magnet are
made from NdFeB.
78. The permanent magnetic actuator of claim 63, wherein the inner
annular magnet, middle annular magnet, and outer annular magnet are
made from SmCo.
79. The permanent magnetic actuator of claim 63, wherein the
conductive coil is wound in a pancake winding.
80. The permanent magnetic actuator of claim 63, wherein the
conductive coil is wound in a solenoidal winding.
81. The permanent magnetic actuator of claim 63, wherein the
conductive coil is wound in a toroidal winding.
82. The permanent magnetic actuator of claim 63, wherein the
conductive coil is wound with two toroidal windings, such that the
windings have the same poloidal sense but opposite toroidal
sense.
83. The permanent magnetic actuator of claim 63, wherein the
conductive coil is wound with two toroidal windings, such that the
windings have the same toroidal sense but opposite poloidal
sense.
84. A method for creating a magnetic force comprising: creating a
magnetic field engulfing a conductive coil, said magnetic field
comprising the superposition of a first magnetic field curling from
an inner ring of a magnetic array outward to an outer ring of said
magnetic array, and a second magnetic field pointing radially
outward from a middle annular ring of said magnetic array; and
applying a current through said conductive coil.
Description
FIELD OF THE INVENTION
The present invention relates to the field of actuators, and in
particular, direct drive actuators employing a radial magnetic
field acting on a conducting coil.
BACKGROUND OF THE INVENTION
There is currently a large effort devoted to the miniaturization of
unmanned aerial vehicles (UAVs). Through rapid advancement in the
miniaturization of essential elements such as inertial measurement
units, sensors, and power supplies, Micro Air Vehicles (MAVs) have
become a reality. However, little research has focused on the
miniaturization of control surface actuators. Instead, MAV
developers have used hobby-quality actuators. These actuators are
typically too big, too heavy, too slow, inefficient and unreliable
for use in MAVs. Therefore, there exists a need for reliable
actuators that are designed to address the following issues: size,
weight, bandwidth, torque, reliability, voltage, rate and position
saturation.
The next generation of MAVs are described by the Defense Advanced
Research Projects Agency (DARPA) as being less than 15 cm in
length, width or height. This physical size renders this class of
vehicle at least an order of magnitude smaller than any missionized
UAV developed to date. Equally as important, the weight of the
actuators should account for less than 5% of the total weight of
the vehicle. Lincoln Lab investigated one example of a vehicle of
this type. For a ten-gram concept vehicle, propulsion not only
consumed 90 percent of the power, but also 70% of the weight
budget. The remaining 30% of the weight budget accounted for the
control surface actuators, as well as the flying structure, camera,
atmospheric sensor array, and other avionics systems.
Past efforts to conform to MAV standards, such as Aerovironment's
Black Widow, have approached DARPA's requirements with the flying
wing approach. The flying wing achieves long flight duration;
however, its low chord Reynolds number airfoils (30,000 to 70,000)
operate in an aerodynamic regime far from the predictable
aerodynamics of larger vehicles. The flying wing is highly
susceptible to wind shear, gusts and roughness produced by
precipitation. To achieve flight stability in this aerodynamic
environment, the MAV must be capable of rapid actuation or have a
high bandwidth. Intimately connected to the bandwidth, the torque
requirement consists of maintaining an aerodynamic control surface
in place. The actuators must not only be capable of rapid
acceleration, but must also have adequate travel and peak angular
velocity, thus satisfying the rate and position saturation
requirements for MAV control surface actuation.
There are several approaches to determining the best actuator for
MAVs. The current approach relies on available commercial
off-the-shelf actuators. Given the current state of technology,
many possible options, though substandard, exist to fulfill the
microactuation requirements of MAVs. Among the possibilities are
packaged servos, commercial motors, voice coil motors, HDD
microactuators, and nanomuscles.
The first option is servo actuators. However, low bandwidth is the
main drawback with packaged servo actuators. The approach in these
actuators is to minimize the weight by using the smallest
high-speed motors available, then gearing the speed down through an
array of plastic gears while at the same time increasing the
torque. In general, the equivalent motor inertia and frictional
force on the driven shaft side increases by a factor of the gearing
ratio squared, further reducing bandwidth. Such gearing not only
introduces power loss, but also introduces backlash. Backlash
causes unexpected dynamics in systems, such as the control surface
for an aerial vehicle, which requires precise position control and
undergoes frequent change in direction.
Further, the torque provided by commercial hobby servos is more
than necessary for MAVs. Saturation occurs at relatively low speeds
because the official specifications for these actuators do not
indicate bandwidth; rather, the time for the actuator to travel 60
degrees is given. Such a degree of mismatch in performance
requirements is unacceptable in a system with extremely tight size,
weight and performance requirements.
Rather than using cased servos, using motors directly for actuation
is another option. The advantage is that motors can be made very
small. In particular, Faulhaber and Smoovy produce motors on the 2
and 3 mm scale. The overall disadvantage is that the motors are
built for continuous operation and very high velocity at the
expense of torque. This necessitates some form of transmission, and
therefore, power losses and backlash between the motor and the
final drive stage occur. Another drawback is that the very smallest
motors are brushless polyphase devices, which require external
controls.
Nanomuscles are linear actuators commercially manufactured near the
size factor required for MAV applications. Nanomuscles are
attractive devices for microactuation because they are small,
light, and are capable of very large forces over adequate stroke (4
mm). The major drawback, however, is that the actuation time is
about one-half of a second. Another drawback is that the
nanomuscles are only capable of contraction, thus requiring two
units for full actuation.
Among the many types of actuators such as speakers, rotary, etc.,
the voice coil actuator family also encompasses hard disk drive
(HDD) actuators. The boom of the computer industry pushes for
continual improvements in HDD actuators. The goal of the HDD
manufacturers is higher data storage capacity achieved through
increased head position resolution and bandwidth. The most common
method for high bandwidth HDD actuation is the combination of a
high travel, low-resolution voice coil actuator in series with a
low travel, high-resolution microactuator.
The voice coil alone achieves high bandwidth through direct drive
actuation and low arm inertia. The force of actuation in voice coil
motors, as in all direct drive motors, is purely electromagnetic;
the only source of friction is the support bearing for the arm or
object being moved. The main drawback to the voice coil design is
the heavy weight of non-moving components. For data storage,
overall weight reduction is not a vital requirement; therefore,
only portions of the magnetic field and current are used at any
given time for actuation.
Among the most common microactuators are those used on the tips of
read heads for HDDs. These microactuators are divided into two
families: piezo and electrostatic. Advantages of these actuators
include a high bandwidth on the order of kilohertz and a very
lightweight and small package. On the other hand, the actuator is
so small that the effective stroke only extends on the order of
micrometers. Another drawback to HDD microactuators for MAVs is
that both piezo and electrostatic slider actuators require near 80
Volts for full travel. Piezoelectric multilayer bender actuators
provide higher travel on the order of a millimeter; however, they
still require high voltages.
SUMMARY OF THE INVENTION
The present invention provides a high intensity radial field (HIRF)
magnetic array and actuator employing direct drive technology,
which operates particularly well in micro scale applications.
A nested magnetic array consistent with the invention comprises an
outer magnet with a magnetization pointing in an axial direction; a
middle magnet with a radial magnetization which is pointed either
concentrically inward or outward and is perpendicular to the
magnetization of the outer magnet; and an inner magnet with a
magnetization pointed anti-parallel to the magnetization of the
outer magnet.
In one embodiment, a permanent magnet actuator comprises a first
magnetic array comprising nested outer, middle and inner
cylindrical magnets, wherein the outer annular magnet of the first
magnetic array has a magnetization pointing in an axial direction,
the middle annular magnet of the first magnetic array has a radial
magnetization which is pointed either concentrically inward or
outward and is perpendicular to the magnetization of the outer
annular magnet, and the inner cylindrical magnet of the first
magnetic array has a magnetization pointed anti-parallel to the
magnetization of the outer annular magnet; and a conductive coil
having a current located within the volume of conductor, wherein
the magnetic field of the first magnetic array is substantially
radial and perpendicular to the current located in the conductive
coil. The conductive coil may be located above or below the first
magnetic array, depending upon the magnetization direction of the
magnets in the magnetic array.
In another embodiment, a permanent magnet actuator further
comprises a second magnetic array comprising nested outer, middle,
and inner cylindrical magnets, the second magnetic array being
located on the opposite side of the conductive coil from the first
magnetic array, wherein the outer annular magnet of the second
magnetic array has a magnetization pointing in an axial direction
parallel to the direction of the magnetization of the inner
cylindrical magnet of the first magnetic array, the middle annular
magnet of the second magnetic array has a magnetization in the same
direction as the middle magnet of the first magnetic array, and the
inner cylindrical magnet of the second magnetic array has a
magnetization anti-parallel to the magnetization of the outer
annular magnet of the second magnetic array; wherein the conductive
coil is disposed between the first and the second magnetic arrays,
and wherein the magnetic field of the first and the second magnetic
arrays is perpendicular to the current located in the conductive
coil. The coil may comprise at least one wire having a plurality of
turns.
In method form, a method for creating a magnetic force comprises
creating a magnetic field engulfing a conductive coil, the magnetic
field comprising the superposition of a first magnetic field
curling from an inner ring of a magnetic array to an outer ring of
the magnetic array, and a second magnetic field pointing radially
outward from a middle ring of the magnetic array; and applying a
current through the conductive coil.
The conductive coil may have a winding that is variously
configured, e.g., pancake-shaped, solenoidal, or toroidal. The coil
may comprise more than one winding (e.g., two windings wound in
opposing directions) for use, e.g., in a two degree-of-freedom
actuator, with independently controlled orthogonal axes.
Further, in an exemplary actuator consistent with the present
invention, the arrays may be canted to permit the toroidal winding
to expand, affording control over the spread of the magnetic field
in the gap.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial cutaway schematic view of an exemplary HIRF
permanent magnet array consistent with the present invention;
FIG. 2 is a plot illustrating the radial (horizontal) magnetic
field intensity from an exemplary permanent magnet array consistent
with the present invention;
FIG. 3 is an arrow plot illustrating the radial magnetic field
orientation above an exemplary magnetic array consistent with the
present invention in the conductive coil region, wherein the lower
rectangle is the magnetic disk array seen from the edge, and the
upper rectangle is the conductive coil seen from the edge;
FIG. 4 is a graph illustrating force over distance away from the
magnetic array surface in an exemplary actuator consistent with the
present invention, wherein Force.sub.k corresponds to the force
with one magnetic array in use, and Force2.sub.k corresponds to the
force with first and second magnetic arrays in use;
FIG. 5 is a schematic 3-D cut-away view of an exemplary actuator
consistent with the present invention;
FIG. 6 is a side sectional view of the actuator of FIG. 5, showing
HIRF magnetization, magnetic field, current and force
direction;
FIG. 7 is a side sectional view of an exemplary actuator having
first and second magnetic arrays, in another embodiment of the
present invention;
FIG. 8 is a side sectional view of an exemplary actuator in another
embodiment of the invention, with ferromagnetic flux posts;
FIG. 9 is a side view of the inner magnet of an exemplary HIRF
permanent magnet array consistent with the present invention,
illustrating the magnetic field lines created by the magnetization
of the inner cylinder;
FIG. 10 is a side view of the middle annular magnet of an exemplary
HIRF permanent magnet array consistent with the present invention,
illustrating the magnetic field lines created by the magnetization
of the middle ring;
FIG. 11 is a side view of the outer annular magnet of an exemplary
HIRF permanent magnet array consistent with the present invention,
illustrating the magnetic field lines created by the magnetization
of the outer ring;
FIG. 12A is a top view of an exemplary conductive coil consistent
with the present invention, having a pancake-shape winding;
FIG. 12B is a side cross-sectional view of the exemplary conductive
coil of FIG. 12A;
FIG. 13A is an oblique view of another exemplary conductive coil
consistent with the present invention, having a solenoidal
winding;
FIG. 13B is a side cross-sectional view of the exemplary conductive
coil of FIG. 13A;
FIG. 14 is a side cross-sectional view of still another exemplary
conductive coil consistent with the present invention, having a
toroidal winding;
FIG. 15 is an oblique sectional view of yet another exemplary
conductive coil consistent with the present invention, having a
toroidal winding and having utility in an exemplary two
degree-of-freedom acutator; and
FIG. 16 is a side cross-sectional view of a plurality of exemplary
canted magnetic arrays consistent with the present invention,
disposed as in an exemplary actuator.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic view of an exemplary high intensity radial
field (HIRF) magnetic array 22 consistent with the present
invention. The HIRF magnetic array 22 comprises two nested annular
magnets 10, 12 and an inner cylindrical magnet 14, which could also
be annular, which are magnetized in the orientations shown in FIG.
1 or in their opposite orientations, respectively. The outer
annular magnet 10 has a magnetization pointing axially out of the
bottom of the array; the magnetization of the middle ring 12 is
perpendicular to the magnetization of the outer ring 10 and points
in the inward radial direction; and the magnetization of the inner
cylinder 14 points anti-parallel to the outer ring, i.e., out of
the top of the array. Magnets 10 and 14 are always anti-parallel to
each other and may be magnetized in the opposite directions, and
the middle annular magnet 12 may be magnetized in either radial
direction--in both cases, depending on the side axially where the
magnetic field is to be intensified.
The magnetic fields created by each of the three nested magnets are
shown in FIGS. 9-11. FIG. 9 shows the direction of the magnetic
field lines created by the inner cylinder 14. The magnetic field
for the inner cylinder 14 points vertically upward inside the
cylinder 14 and curls around to the outside of the cylinder 14 from
the top to the bottom as represented by vectors A, B, and C.
FIG. 10 shows the magnetic field of the middle annular magnet 12.
The magnetization points radially inward inside the ring 12. The
direction of the magnetic field outside the ring 12 is represented
by vectors D and E.
The magnetic field of the outer annular magnet 10 is illustrated in
FIG. 11. The magnetization of the outer ring 10 is vertically
downward. The direction of the magnetic field is represented in
FIG. 11 by vectors F, G and H.
Superposing the fields of the three magnets 10, 12, 14 will produce
the manetic field of the magnetic array 22 shown in FIGS. 2 and 3.
Vectors A, D and F represent the fields of the three magnets 10,
12, 14 above the array, respectively. These three vectors are all
pointing in the same direction above middle magnet 12, and
therefore, the magnetic fields add together to create a high
intensity magnetic field pointing radially outward. Vectors B and G
represent the magnetic field along the side of the array 22. These
two vectors are pointing in opposite directions and thus partially
cancel one another. Finally, vectors C, E and H represent the field
of each magnet 10, 12, 14 below the array. The field E of the
middle ring 12 points in the opposite direction from the fields C,
H of the two other rings 10, 14. Therefore, there is a partial
cancellation of the magnetic field in this area. Consequently, only
a very weak magnetic field exists below the array 22.
The key concept is the vectorial addition of fields increasing the
radial field above the array while decreasing the radial field
below the array. By reversing the magnetization of the middle
magnet, the high magnetic field can be shifted from above to below
the array. Alternatively, the magnetization vectors of both the
inner and outer magnets could be reversed to control the location
of the large radial magnetic field.
A specific advantage of this magnet configuration is the shifting
of magnetic field from unused space away from the conductor to
where a conducting coil is situated. This results in an efficient
usage of the total magnetic field from the permanent magnets. FIG.
2 shows the intensity of the radial (horizontal) component of the
magnetic field. It should be noted that the magnetic field is
strong where a coil is above the magnetic array, while
comparatively non-existent below the array.
In one embodiment, this exemplary HIRF magnetic array 22 may be
combined with such a conductive coil 20 to form a HIRF actuator, as
illustrated in the exemplary actuator of FIG. 5. The coil 20 is
simply a hoop with multiple turns of wire and may have an average
radius equal to the average radius of the middle,
radially-magnetized magnet 12. Because the radial field is always
orthogonal to the conductive coil, there are no unused end turns,
thus increasing the actuator's ohmic efficiency. All the current in
the conductor contributes to moving the coil axially toward or away
from the magnetic array, dependent upon the direction of the
current.
Turning now to FIGS. 12A and 12B, one exemplary coil winding 600 is
illustrated, wherein the coil 600 has a plurality of turns of wire
601 and has a pancake-shaped winding. Alternatively, as illustrated
in FIGS. 13A and 13B, another exemplary coil winding 700 is
illustrated, wherein the coil 700 has a plurality of turns of wire
701 and has a solenoidal winding.
Another important aspect of the magnet array is that the field
extends radially above the magnets, as illustrated in FIG. 3, an
arrow plot of the magnetic field orientation above the magnetic
array in the conductive coil region, wherein the lower rectangle 30
represents the magnetic array 22 and the upper rectangle 32
represents the conductive coil 20. As shown in FIG. 3, in this
exemplary embodiment of the present invention, the magnetic field
curls from the inner magnetic field through the conductive coil
into the outer ring. If the first magnetic field curls outward from
the inner ring to the outer ring, then the second magnetic field
should also point radially outward, i.e., the middle magnet
magnetization is radially inward and its magnetic field outside the
magnet is outward.
The magnetic field shown in FIG. 3 can be used with the Lorentz
force law to calculate the direction of the force on the conductive
coil. The Lorentz Force law states that F=qv*B, where q is the
charge, v is the velocity of the charge, and B is the magnetic
field. In the left portion of the coil, as illustrated in the
exemplary embodiment of FIG. 6, the direction of the current I
originates from the page (toward the reader hereof), and the
magnetic field lines B curl from right to left. Thus, using Lorentz
force law and the right-hand rule, the magnetic force F pushes the
conducting coil 20 toward the magnetic array 22. Similarly, on the
right side of the coil 20, the current flows into the page (away
from the reader hereof), and the magnetic field curls from left to
right, therefore creating a downward force. Line 42 of the graph of
FIG. 4 shows the magnitude of the force on the coil 20 with respect
to distance away from a single magnet array for a given current.
The stroke of this actuator is dependent on the maximum distance
between the coil 20 and magnetic array 22 in which a significant
force can still be applied.
Those skilled in the art will recognize that, although the
foregoing embodiment describes a HIRF actuator with reference to a
magnetic array below the coil, the magnetic array could,
alternatively, be located on either side of or above the conductive
coil.
As shown in FIG. 7, in another embodiment of the present invention,
both a top and bottom magnetic array are utilized for a greater
radial magnetic field, and hence, a greater axial force per unit
current. In the embodiment shown in FIG. 7, a top magnetic array
222 is disposed above the conductive coil 120, and a bottom
magnetic array 122 below the coil 120. The top magnetic array 222
is magnetically inverted with respect to the bottom array 122. That
is, the top magnetic array 222 is positioned so that the direction
of the magnetic field in the top inner coil 214 is anti-parallel to
the magnetic field in the bottom inner coil 114. Therefore, as seen
in FIG. 7, the radial magnetic field from the top magnetic array
222 reinforces the radial magnetic field of the bottom array 122.
This creates a greater force per unit current. Line 40 of FIG. 4
shows how the force varies over distance for this exemplary
embodiment of the invention.
As shown in FIG. 8, in certain embodiments of the present
invention, one or more annular ferromagnetic flux posts 80 may be
disposed between top 322 and bottom 422 magnetic arrays. The
annular flux posts 80 are used to increase and control the radial
magnetic field, as a function of position in the gap. Accordingly,
the surface of the posts may be shaped in a known manner similar to
magnetic pole faces, e.g., annular in shape, to optimize the
magnetic field distribution within the gap. Thereby, the actuator
response is made more linear than it would be without the flux
posts 80, which aid in shaping the flux. Those skilled in the art
will recognize that an actuator arm (not shown) may be adapted to
penetrate the flux posts according to known techniques.
The magnets described herein may comprise rare earth magnets, e.g.
NdFeB or SmCo. Since magnetic field superposition is a
consideration, ceramic and AlNiCo magnets may be less desirable for
some applications, as they do not have substantially linear
responses (e.g., as compared to NdFeB). However, since ceramic
magnets are linear over a portion of their operating curve, they
may have potential utility in certain non-critical embodiments of
the invention, e.g. actuators for toys.
With reference to FIG. 14, in a third exemplary coil winding
embodiment, the coil 800 has a plurality of turns of wire 801 and
has a toroidal winding. This toroidal winding creates different
forces than either of the pancake-shaped or solenoidal windings
described above.
The Lorentz force is dependent upon the vector cross-product of the
current and the magnetic field, F=.intg.I d1.times.B. The
cylindrical Halbach magnet array described produces magnetic field
of the form (B.sub.r, 0, B.sub.z). For a pancake or solenoid
winding, the coil vector I d1 is of the form (0, I d1.sub..theta.,
0). Therefore, as is well known to those skilled in the art, the
force is F=r(J.sub..theta. B.sub.z)+.theta.(0)+z(J.sub..theta.
B.sub.r). The radial force component generally integrates to zero
leaving the axial force as the major force component.
For a toroidal winding, within the magnetic field of the array the
coil vector I d1 is of the form (I d1.sub.r, 0, I d1.sub.z).
Therefore, the force is:
This force creates a torque about the z-axis, T.sub.z =r
I.multidot.(B.sub.z d1.sub.r -B.sub.r d1.sub.z).
It is noted that a toroid with N turns about the minor axis
(poloidal axis) executes a single turn about the major axis
(toroidal axis). This single turn would produce an axial force
according to the first embodiment. Controlling N allows the ratio
between the axial force and torque to be varied.
Turning now to FIG. 15, an exemplary conductive coil 900 consistent
with the present invention is illustrated, comprising two toroidal
windings 2200, 2300. The windings 2200, 2300 are wound
concentrically such that they have the same poloidal sense but
opposite toroidal sense, with N=11. Then, a positive current in
winding 2200 is in the same poloidal direction as winding 2300, and
the respective torques Q, R add vectorially, producing twice the
torque of a single winding. The toroidal currents, however, cancel,
thereby producing no axial force. This is the state shown in FIG.
15. Alternatively, if a positive current is introduced in winding
2200 but a negative current is introduced in winding 2300, then the
torques Q, R tend to cancel, and the axial forces add. Hence, a two
degree-of-freedom (2 DOF) actuator results, with independently
controlled orthogonal axes. Clearly, any even number of windings
can be evenly split in such a manner (i.e., half of the windings
wound one way, the other half the other way).
Exemplary dimensions of a magnetic array (e.g., as shown in FIG. 1)
used in an HIRF actuator for MAVs consistent with the present
invention may be as follows: an inner magnet having a radius
r.sub.1 =2 mm and a height of 1 mm; a middle magnet having an inner
radius=r.sub.1, an outer radius r.sub.2 =r.sub.1 =0.83 mm, and a
height of 1 mm; and an outer magnet having an inner radius=r.sub.2,
an outer radius r.sub.3 =r.sub.2 +0.63 mm, and a height of 1 mm.
Here, the coil dimensions may be: inner radius=r.sub.1, outer
radius=r.sub.1 +0.83 mm, and a height t=0.5 mm. It should be noted
that the flux area of the three magnets is desirably constant
(although not necessary), and the flux areas may be described by
the following equations:
A3=.pi.*(r.sub.3.sup.2 -r.sub.2.sup.2)(top)
Further, the (vertical) gap between opposing magnet arrays is Z=1.6
mm, the ampere-turns of the coil are NI=100 amps. By magnetic field
analysis, the radial flux density at the center of the conductor is
B_rad=0.45 Tesla, and the corresponding Lorentz (vertical) force is
0.68 Newtons=F=NI*L*B_rad, where L=2*.pi.*(r.sub.1 +(r.sub.2
-r.sub.1)/2) is the length of the center of the conductor. The
stroke is Z-t=1.1 mm.
It should be understood that the aforementioned geometry and
dimensions are merely exemplary, and it is contemplated that the
present invention covers other embodiments of arrays, actuators,
and actuation systems not specifically illustrated or described
herein, having alternative geometries. For example, while the coil
dimensioned as described above may produce a high level of heat and
therefore be suitable for an aerodynamic application (e.g., high
forced convection) or a duty cycle of 10% or less, it should be
recognized that alternative coil sizes may be selected based on
factors such as desired thrust (force) and heating.
With reference now to FIG. 16, in yet another embodiment of the
present invention, a plurality of canted magnetic arrays 2400, 2500
consistent with the present invention are illustrated, disposed as
in an exemplary actuator. Each array 2400, 2500 has inner 2414,
2514, middle 2412, 2512, and outer 2410, 2510 magnets. In this
embodiment, the surface of each magnetic array 2400, 2500 is angled
(at an angle .alpha.) to permit the toroidal winding to expand.
This affords the designer some control over the spread of the
magnetic field in the gap using the magnetic field characteristics
associated with the Maxwell equation .gradient..multidot.B=0. The
angle .alpha. may be positive or negative.
Those skilled in the art will recognize that the inner magnet of an
array consistent with the present invention may be either an
annular or cannulated member (i.e., hollow), or alternatively, a
solid cylindrical member. A magnetic array consistent with the
invention having an inner magnet that has an aperture along its
central axis may be adapted for fixation to another component as is
part of an actuation system, wherein a J-shaped "umbrella" hook
disposed within the aperture may be used to mount the array and/or
coil. Of course, it is contemplated that other mounting means could
alternatively be used for fixation of the array.
The foregoing embodiments are intended to be illustrative and not
limiting. Numerous other embodiments will be apparent to those
skilled in the art. All such alternative embodiments are included
in the broad principle of the invention, as defined in the
following claims.
* * * * *